Methods and systems for measuring atmospheric water content

ABSTRACT

Methods and systems for measuring atmospheric water content, are provided. The method includes measuring a first air temperature and a first air pressure at a first location in a compressor, measuring a second air temperature and a second air pressure at a second location in the compressor, computing a ratio of specific heats from the first and second air temperatures and the first and second air pressures, and determining an atmospheric water content from the ratio of specific heats.

BACKGROUND OF THE INVENTION

This invention relates generally to methods and systems for measuringatmospheric conditions and more particularly, to methods and systems forcollecting atmospheric weather data using an aircraft.

An important obstacle to improved forecasting is lack of data aboutwater content in the troposphere. Water content of an air mass canchange rapidly during storms, over moist soil, or over bodies of watersuch as oceans. An inability to track changes in water content in theseand other areas contributes to inaccurate weather forecasts.

Existing methods for detecting and quantifying water vapor areinadequate because they can only be implemented on a local scale overland thereby leaving vast gaps in global meteorological continuity. Thelargest gaps occur over oceans where most atmospheric conditionsoriginate. Although the existing atmospheric sensing systems listedbelow exhibit high resolution capabilities on a local scale, it is notpractical to deploy such systems on a global scale because they areexpensive to implement or maintain on a global scale and they lackadequate temporal and/or spatial resolution for realistic use on aglobal scale.

Currently, a primary source of water vapor measurements are ground-basedhumidity sensors and balloon-borne sensors called “radiosondes.”Radiosonde data have high quality, but have relatively poor spatial andtemporal resolution. The radiosonde, an expendable balloon-borneinstrument package that relays temperature, humidity, and pressure datato a ground receiver by radio signals, is the traditional cornerstone ofthe worldwide operational weather analysis and prediction system throughdeployments twice daily at several hundred sites around the world.However, the twice daily radiosonde deployments are primarily over landand are sparsely distributed due to cost considerations. No above-groundmeasurements are available during intervals between launches or atlocations far from radiosonde launch points. For these reasons,radiosonde data is too costly and localized to support high resolutionglobal meteorology.

A limited number of commercial air carriers presently provide real-timewind, pressure, temperature, and humidity readings around the world aspart of a system called Aeronautical Communications Addressing andReporting System (ACARS). Although the ACARS system provides about10,000 readings per day world wide at a cost about 100 times less thanthe recurring cost of radiosondes, the vast majority of ACARS readingsare around airports and along common flight paths at established cruiseflight levels which limits the spatial scope of this otherwise valuabledata.

Earth-based Differential Absorption Lidar (DIAL) and Raman Lidar systemsare used to provide wind and water vapor profiles in remote areas.However, such systems are not economic to install and maintain, they donot penetrate cloud cover, and the lasers used are highly energized andare therefore not eye-safe.

Water vapor radiometers are instruments that measure microwave energyemitted by the atmosphere to estimate zenithal integrated water vapor.Integrated water vapor is a measure of the depth of liquid water thatwould result if a column of water vapor were condensed into liquidwater. Zenithal integrated water vapor (IWV), also known as PrecipitableWater Vapor (PWV), is the integrated water vapor in a vertical columndirectly overhead an Earth-based measuring device. Earth-basedupward-looking water vapor radiometers estimate PWV by measuringradiative brightness temperatures against the cold background of space.However, upward-looking water vapor radiometers must be “tuned” to localconditions using independently obtained PWV data, and although theygenerally exhibit good temporal resolution in relatively clearatmospheric conditions, they provide only localized PWV over land.Further, unless properly equipped, upward-looking radiometers arevirtually useless in rain. Alternatively, satellite-based,downward-looking radiometers perform well over water and consistenttemperature land masses by viewing microwave emissions from theatmosphere and underlying Earth's surface. Although downward-lookingradiometers generally exhibit good spatial resolution they exhibit poortemporal resolution and perform poorly over most land masses. In eithercase, water vapor radiometers as a whole are not practical for globalscale meteorology due to their cost, limited view, and performancecharacteristics.

Fourier Transform Infrared Radiometer (FTIR) systems can provide highresolution satellite-based and Earth-based temperature and water vaporprofiles by using a recursive solution of the radiative transferequation to provide a vertical profile from the ground up. Although thismethod can provide vertical resolution of several hundred meters to akilometer in the lower troposphere, the system exhibits poor performancein the presence of cloud cover and infrared active gases such astropospheric ozone.

Unmanned Air Vehicles (UAV's) provide high resolution data in regionsinaccessible to other systems discussed above. However, unmannedaircraft are too costly for continuous global sensing, they lackadequate spatial and temporal resolution, and are typically onlyjustified in specialized research applications.

Additional water content measurements are available from satellites andfrom a few specially-equipped airliners operated under a NASA programcalled Tropospheric Airborne Meteorological Data Reporting (TAMDAR).Satellite data are unreliable because it is difficult for satellites tocorrectly resolve the altitude profile of moisture, especially whenclouds are present. TAMDAR uses humidity sensors mounted on the outsideof small, regional airliners. These sensors continuously measurehumidity and temperature as the aircraft ascend and descend through thetroposphere. This provides better spatial and temporal resolution thanradiosondes. Though this approach has been shown to be technicallyeffective for improved weather forecasts in the northeastern US, theadditional weight and drag and the need for FAA certification of eachtype of sensor package on each type of aircraft makes this solutioncostly, which has limited the expansion of existing systems to otherregions.

BRIEF DESCRIPTION OF THE INVENTION

In one embodiment, a method of measuring atmospheric water contentincludes measuring a first air temperature and a first air pressure at afirst location in a compressor, measuring a second air temperature and asecond air pressure at a second location in the compressor, computing aratio of specific heats from the first and second air temperatures andthe first and second air pressures, and determining an atmospheric watercontent from the ratio of specific heats.

In another embodiment, an atmospheric monitoring system includes acompressor and at least one compressor sensor coupled to the compressor,wherein the sensor is configured to acquire atmospheric data from airchanneled through the compressor.

In yet another embodiment, a method of forecasting weather includesacquiring atmospheric data from a gas turbine engine onboard an aircraftduring flight, processing the atmospheric data to determine an amount ofwater content in the atmosphere, transmitting at least one of theatmospheric data and the amount of water content to a weather forecastmodel, and predicting weather based on either one or both datasets.

In still another embodiment, a method of forecasting weather includesdetermining a specific heat of a volume of air at a first location in agas turbine engine, determining a specific heat of the volume of air ata second location in the gas turbine engine, and determining a watercontent of the volume of air using the specific heat of the volume ofair at the first location and the second location.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of an exemplary embodiment of a system forcollecting weather related data and monitoring the performance of gasturbine engines mounted on an aircraft;

FIG. 2 is cross-sectional view of a gas turbine engine in accordancewith an exemplary embodiment of the present invention;

FIG. 3 is a graph of a humidity ratio versus a ratio of specific heatsthat may be used with system shown in FIG. 1;

FIG. 4 is a data flow diagram for determining water content in air usingmeasured parameters from a gas turbine engine; and

FIG. 5 is a map of the United States illustrating exemplary aircraftroutes between various airports which can be used as collection pointsfor weather data in accordance with system shown in FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 is a block diagram of an exemplary embodiment of a system 100 forcollecting weather related data and monitoring the performance of gasturbine engines 102, 104 mounted on an aircraft 106. Although twoengines 102 and 104 are shown in FIG. 1, it should be noted thataircraft 106 could have additional engines mounted thereon. Accordingly,data collection for such additional engines would be accomplished in amanner substantially similar to that for engines 102 and 104. Therefore,only engines 102 and 104 and the associated equipment will be describedherein. Furthermore, it should be noted that the system 100 is describedin connection with an aircraft only by way of example. In addition toaeronautical applications, the present invention is applicable to otherapplications of gas turbine engines, including marine and industrialapplications.

System 100 includes an electronic engine controller (EEC) 108, such as afull authority digital engine control (FADEC), although othercontrollers can be used, associated with each engine 102, 104 and anonboard aircraft data storage device 110. Conventional engine datasensors 112 and aircraft data sensors 114 are provided to sense selecteddata parameters related to the operation and performance of engines 102,104 and/or aircraft 106. The engine data sensors 112 and aircraft datasensors 114 can comprise any group of sensors that monitor dataparameters of interest. In addition to aircraft parameters such asambient temperature, air speed and altitude, engine parameters typicallyinclude exhaust gas temperature, oil temperature, component temperaturessuch as high pressure turbine shroud temperature, engine fuel flow, corespeed, an engine inlet pressure (P0) and an engine inlet temperature(T12) measured upstream of the fan at the engine inlet, and a compressordischarge temperature (T3) and a compressor discharge pressure (P3)measured downstream of the engine high pressure compressor, a turbineexhaust pressure, fan speed, and other engine parameters.

Each ECU 108 receives signals from corresponding engine data sensors 112and the aircraft data sensors 114 as is known in the art. In response tothese and other inputs, ECUs 108 generate command signals to operateengine actuators, such as hydro-mechanical units (not shown) that meterthe flow of fuel to respective engines 102, 104. Each ECU 108 alsooutputs data signals to aircraft data storage device 110. Aircraft datastorage device 110, which can be any conventional device such as aflight data recorder, quick access recorder, or any other type ofin-flight data storage device, has a relatively large data storagecapacity for storing the data signals. Aircraft data storage device 110could also contain processing capability to analyze data in-flight andonly send the necessary maintenance messages to an aircraft centralizedmaintenance computer (not shown). Aircraft data storage device 110 alsoreceives signals from aircraft data sensors 114.

System 100 includes an algorithm that processes the data signals formonitoring engine performance characteristics. The monitoring algorithmcan be implemented in a number of ways. For example, the monitoringalgorithm could be implemented on the ECUs 108 wherein the data signalsare processed as they are received by the ECUs 108. Alternatively, themonitoring algorithm could be implemented on aircraft data storagedevice 110. In this case, the data signals would be processed afterbeing transferred to aircraft data storage device 110. Anotheralternative is to implement the monitoring algorithm on a ground stationcomputer 116, such as personal or workstation computer. The data signalsstored in aircraft data storage device 110 during a flight aredownloaded to ground station computer 116 for processing. This transfercan be accomplished after the flight via a communications link 118including use of a removable computer-readable medium, such as a floppydisk, CD-ROM or other optical medium, magnetic tape or the like, or amultimode communication link that may include a wireless portion. It isalso possible to remotely transmit the data signals directly to groundstation computer 116 during flight operations for real-time processing.The signals may also be sent to other vehicles and/or facilities such asother aircraft 120, ships 122, and satellites 124 via link 118.Additionally, each of aircraft 120, ships 122, and satellites 124 maycommunicate between each other using separate communication links 126. Acontinuous and contemporaneous relaying of atmospheric informationbetween aircraft 106, ground station computer 116, other aircraft 120,satellites 124 and ships 122, or other ocean-based vessels or structuresconstitutes in part an atmospheric data network accessible to aplurality of users world-wide. With any implementation, the monitoringalgorithm can be stored on one unit, for example, ECU 108, aircraft datastorage device 110, or ground station computer 116 and accessed fromthere, or alternatively, it could be accessed from a removablecomputer-readable medium inserted into the appropriate drive of theunit. The monitoring algorithm could also be accessed via the Internetor another computer network. As used herein, the term “computer-readablemedium” refers generally to any medium from which stored data can beread by a computer or similar unit. This includes not only removablemedia such as the aforementioned floppy disk and CD-ROM, but alsonon-removable media such as a hard disk or integrated circuit memorydevice in each ECU 108, aircraft data storage device 110, or groundstation computer 116.

Further examples of ground station computer 116 include internationalweather services, National Oceanic and Atmospheric Administration(NOAA), national military weather services, international militaryweather services such as NATO and other alliances, the national weatherservice, and other commercial users of weather information.

During operation, sensors 112 collect atmospheric information from atleast one of engines 102, 104 and begin processing the data by, forexample, transferring the data in whole or in part to ground stationcomputer 116, other aircraft 120, satellites 124 and ships 122 todetermine the atmospheric humidity conditions surrounding aircraft 106.By time and location stamping the atmospheric information at a pluralityof positions along the various flight paths of the aircraft that are apart of system 100 a humidity profile of a large portion of theatmosphere can be determined. Aircraft 106 may preprocess at least aportion of the atmospheric information and may store the information onboard or may transmit the information in real-time to be used by groundstation computer 116, other aircraft 120, satellites 124, and ships 122.

In the exemplary embodiment, the algorithm includes the capability ofcontinuously determining atmospheric weather parameters by using one ormore of engines 102 and 104 as a sensor to derive atmospheric weatherparameter values from existing aircraft engine collected data. Forexample, in the exemplary embodiment, engines 102 and/or 104 are used asa humidity sensor to determine an amount of atmospheric water vaporcontent entering the engine and therefore the amount of atmosphericwater vapor content in the air surrounding aircraft 106. In theexemplary embodiment, pressure (P) and temperature (T) measurementstaken from the turbine engine's inlet and compressor stages are used todetermine atmospheric water vapor content. The determined water contentvalue and a time and location at which the measurements were made aretransmitted to, for example, ground station computer 116 forassimilating humidity measurements into weather forecasts.

FIG. 2 is cross-sectional view of a gas turbine engine 102 in accordancewith an exemplary embodiment of the present invention. Engine 102includes a fan assembly 202 including a containment 204 and a pluralityof fan blades 206. Outlet guide vanes (OGV) 208 extend between aft fancase 210 and an inner casing 211. A fan frame 212 radially supports aftfan case 210. A four stage orthogonal booster 214 co-rotates with fanblades 206. A variable bypass valve (VBV) extends between fan struts216. Engine 102 includes an engine inlet pressure sensor (P0) and anengine inlet temperature sensor (T12) that measure respective engineprocess parameters upstream of the fan at the engine inlet, and acompressor inlet temperature (CIT) probe T25 and a compressor inletpressure port P25 located upstream from a high pressure compressor 218.

A rear frame 231 of compressor 218 includes a combustor 230 and anigniter plug 232 with a fuel nozzle 234 and an outlet guide vane (OGV)236. It includes a vent seal 238 and 4R/A/O seal 240 and 4R bearing 242and 4B bearing 244. Rear frame 231 also includes a 5R bearing 246 and5R/A/O seal 248, a diffuser 250 and pressure balance seal 252.Compressor rear frame 231 also includes a turbine stage 1 nozzle 254. Acompressor discharge temperature (T3) sensor and a compressor dischargepressure (P3) port provide access to conditions at the compressordischarge. Engine 102 includes a high pressure turbine 260 and a lowpressure turbine 262 that includes a 360° case 264, aerodynamic struts266 that remove swirl from the exit gas and a turbine rear frame 268formed as a one piece casting.

In operation, air flows through fan assembly 202 and a first portion ofthe airflow is channeled through booster 214. The compressed air that isdischarged from booster 214 is channeled through compressor 218 whereinthe airflow is further compressed and delivered to combustor 230. Hotproducts of combustion (not shown) from combustor 230 are utilized todrive turbines 260 and 262, and turbine 262 is utilized to drive fanassembly 202 and booster 214 by way of a shaft 270.

Many of the components of engine 102 are monitored by process sensorsand structural force sensors that generate signals during various flightmodes including initial take-off, level flight and landing. Such signalsare relayed via the EEC 108 an on-ground maintenance crew and/orseparate remote engine data control center having its own processor.

In the exemplary embodiment, engine inlet pressure (P0) and an engineinlet temperature (T12), compressor discharge temperature (T3) sensorand a compressor discharge pressure (P3) are also used for estimatingatmospheric water content. As air traverses the compressor stages of theengine, its pressure and temperature increase. For air containing littlewater vapor, the value of the specific heat of the air, c, is low. Forair containing more water vapor, the value of the specific heat of theair, c is relatively larger. As a result, a temperature rise for moistair flowing through the compressor is less than the temperature rise fordry air flowing through the compressor. For air containing waterdroplets or ice crystals, overall specific heat, c, is even higher: asthe temperature rises, the ice melts and the water vaporizes. Such phasechanges absorb large amounts of heat, so the temperature rise in thecompressor is even less than the temperature rise for air with a largeamount of water vapor.

To convert pressure and temperature measurements into water content,methods of various embodiments of the present invention, for example,use the equations of isentropic compression to compute a ratio ofspecific heats, a term which is known to those skilled in the art tomean the ratio of c_(p) (specific heat at constant pressure) to c_(v)(specific heat at constant volume). The methods then use the ratio ofspecific heats to determine the water content of the air for example, byusing a look-up table.

FIG. 3 is a graph 300 of a humidity ratio versus a ratio of specificheats that may be used with system 100 (shown in FIG. 1). Graph 300includes an x-axis 302 graduated in units of humidity ratio and a y-axis304 graduated in units of a ratio of specific heats. Graph 300 includesa first trace 306 illustrating a relationship between humidity ratio anda ratio of specific heats at a temperature of approximately 180° C. anda pressure of 0.5 MPa. A second trace 308 illustrates a relationshipbetween humidity ratio and a ratio of specific heats at a temperature ofapproximately 200° C. and a pressure of 0.5 MPa. A third trace 310illustrates a relationship between humidity ratio and a ratio ofspecific heats at a temperature of approximately 240° C. and a pressureof 0.5 MPa. A forth trace 312 illustrates a relationship betweenhumidity ratio and a ratio of specific heats at a temperature ofapproximately 280° C. and a pressure of 0.5 MPa, and a fifth trace 314illustrates a relationship between humidity ratio and a ratio ofspecific heats at a temperature of approximately 320° C. and a pressureof 0.5 MPa.

In the exemplary embodiment, engine 102 operates using a Brayton cyclewherein the compression stage is isentropic. For isentropic compression,the following relationship between pressure and absolute temperatureapplies, where γ is the ratio of specific heats (γ=c_(p)/c_(v)):

$\begin{matrix}{\frac{T_{2}}{T_{1}} = \left( \frac{P_{2}}{P_{1}} \right)^{1 - \frac{1}{\gamma}}} & (1)\end{matrix}$

If equation (1) is solved for γ, a relationship between humidity and theratio of specific heats may be applied to determine humidity frommeasurements of pressure and temperature.

$\begin{matrix}{\gamma = \frac{\ln \left( \frac{P_{2}}{P_{1}} \right)}{{\ln \left( \frac{P_{2}}{P_{1}} \right)} - {\ln \left( \frac{T_{2}}{T_{1}} \right)}}} & (2)\end{matrix}$

The qualitative relationship between the ratio of specific heats andrelative humidity is: as humidity increases, γ decreases. Thisrelationship can be derived from the definition of the ratio of specificheats shown in Equation 3.

$\begin{matrix}{\gamma = \left( \frac{c_{p}}{c_{v}} \right)_{mixture}} & (3)\end{matrix}$

For an ideal gas, enthalpy, h and internal energy, u can be expressedrespectively as:

h=c_(p)T u=c_(v)T   (4)

Therefore, the ratio of specific heats can be rewritten as:

$\begin{matrix}{\gamma = \left\lbrack \frac{h/T}{u/T} \right\rbrack_{mixture}} & (5)\end{matrix}$

The temperature term cancels, and the equation can be rewritten usingthe following relationships for specific enthalpy and specific energy inan air/water vapor mixture, where (t is the humidity ratio.

H/m _(air) =h _(air) +ω·h _(vaper) U/m _(air) =u _(air) +ω·u _(vapor)  (6)

The relationship between γ and the humidity ratio becomes:

$\begin{matrix}{\gamma = \frac{h_{air} + {\omega \cdot h_{vapor}}}{u_{air} + {\omega \cdot u_{vapor}}}} & (7)\end{matrix}$

which, can be solved for the humidity ratio ω as:

$\begin{matrix}{\omega = \frac{{\gamma \cdot u_{air}} - h_{air}}{{\gamma \cdot u_{vapor}} - h_{vapor}}} & (8)\end{matrix}$

Values for h_(air), u_(air), h_(vapor,) and u_(vapor) can be obtainedfrom the ideal gas tables for air and water vapor. FIG. 3 shows theresults of the calculation in equation 7 for a representative pressurevalue of 0.5 MPa. In practice, equation 2 would be used to find γ fromtemperature and pressure. Then γ would be used to calculate ω viaequation 8.

FIG. 4 is a data flow diagram 400 for determining water content in airusing measured parameters from a gas turbine engine. A process receivesinputs 402 of measured parameters of air temperature and static pressureof the ambient air surrounding for example, the gas turbine engine. Theinputs for ambient air temperature and pressure are available frommeasured parameters from the existing T12 temperature sensor and the P0pressure sensor, in the exemplary embodiment. In instances where theseparticular parameters are not measured directly, they may be derived bycomputing the parameter from other measured parameters. The process alsoreceives inputs 402 of measured parameters of air temperature and staticpressure of the compressed air exiting for example, high pressurecompressor 218. Such parameters are also measured using existing engineperformance sensors, T3 and P3, respectively. By using existing engineperformance sensors, new additional sensors are not required to be addedto the aircraft and are not mounted in the airstream surrounding theaircraft contributing to additional aircraft drag.

In the exemplary embodiment, T12, P0, T3, and P3 are used in theequations of isentropic compression 404 described above to determine aratio of specific heats 406 and humidity ratio at the representativepressure and temperature. The processor in the EEC may perform suchcalculation or the T12, P0, T3, and P3 may be transmitted to a secondprocessor for a determination of the ratio of specific heats and/orhumidity ratio. Using the on-board processors or off-board processors todetermine the ratio of specific heats and humidity ratio a water contentof the air surrounding aircraft 100 is determined 408 in real-time andtransmitted to a weather facility where the determined water content isinput 410 into weather prediction algorithms to generate forecast models412 of future weather patterns.

The computations described above can be performed in any of severalplaces: within the Electronic Engine Controller, within anothercomputing device aboard the aircraft, or in a computing device outsidethe aircraft that receives sensor data transmitted to aircraft 100. Thesensor data may be stored aboard the aircraft along with time andlocation data from the aircraft navigation system so it can be retrievedand used to compute water content after the aircraft lands.

Although the description above refers to the isentropic equations, it isunderstood the scope of the various embodiments of the present inventionincludes applying empirical corrections to the computed values toaccount for non-ideal behavior of the gas, or heat transfers in theengine compressor, which make the process not quite isentropic. Otherembodiments of the present invention also include corrections forsolid-to-liquid and liquid-to-gas phase changes when the sensed watercontent exceeds 100% relative humidity at ambient conditions.

FIG. 5 is a map 500 of the United States 502 illustrating exemplaryaircraft routes 504 between various airports 506 which can be used ascollection points for weather data in accordance with system 100 (shownin FIG. 1). Such routes 504 represent the potential data collectioncoverage for determining water content of the air. In the exemplaryembodiment, commercial aircraft enable water content to be continuouslymeasured at low cost along ascents, descents, and routes 504 of flightin the United States 502 and similarly, worldwide. Aircraft traversesuch routes multiple times during a given time period increasing thecollection of water content data by several orders of magnitude comparedto current balloon soundings. Improved water content measurements cansubstantially improve weather forecasts, with particular improvement forpredicting the onset of severe storms driven by convective weather suchas those driven by heat released by gas-liquid phase changes in moistair.

Various embodiments of the present invention facilitates real-time andnear-real time measurements of water content of the air that are usefulfor weather forecast models, particularly over the oceans and landmasses where few sensors are currently available. Various aircraftoperators such as airlines, federal or other national agencies, researchinstitutions, foreign military alliances, and national military airforces benefit from accurate water forecasts for their operation. Foroceanic operators such as the Navy or commercial ship operators,inaccurate weather forecasts can lead vessels into unsafe conditions orcause them to take inefficient routes.

The above-described methods and systems for the continuous measurementof atmospheric water vapor by using an aircraft turbine engine as ahumidity sensor are cost-effective and highly reliable. Pressure andtemperature sensors in the engine's compressor reveal how much thetemperature rises as incoming air is squeezed to higher pressure. Forair containing more water vapor, the temperature rises less. Measuringthe temperature and pressure at two points in the engine compressorpermits computing the moisture content of the air. Because modernturbine engines already have appropriate sensors, no modification toexisting aircraft engine mechanical systems is required, as only asoftware modification is necessary, substantially eliminating any weightor drag penalty. Accordingly, the methods and systems facilitateacquisition of weather related data in a cost-effective and reliablemanner.

While the invention has been described in terms of various specificembodiments, those skilled in the art will recognize that the inventioncan be practiced with modification within the spirit and scope of theclaims.

1. A method for measuring atmospheric water content comprising:measuring a first air temperature and a first air pressure at a firstlocation in a compressor; measuring a second air temperature and asecond air pressure at a second location in the compressor; computing aratio of specific heats from the first and second air temperatures andthe first and second air pressures; and determining an atmospheric watercontent from the ratio of specific heats.
 2. A method in accordance withclaim 1 wherein the compressor is at least one of a portion of a turbineengine and a supercharger.
 3. A method in accordance with claim 1wherein determining an atmospheric water content comprises assumingideal gas behavior and isentropic compression.
 4. A method in accordancewith claim 1 wherein determining an atmospheric water content comprisescorrecting for non-ideal gas behavior.
 5. A method in accordance withclaim 1 wherein determining an atmospheric water content comprisescorrecting for non-isentropic compression.
 6. A method in accordancewith claim 1 wherein measuring a first air temperature and a first airpressure at a first location comprises measuring a first air temperatureand a first air pressure at a first location that is upstream from atleast one of the compressor and a compressor stage.
 7. A method inaccordance with claim 1 wherein measuring a second air temperature and asecond air pressure at a second location comprises measuring a secondair temperature and a second air pressure at a second location that isdownstream from at least one of the compressor and a compressor stage.8. A method in accordance with claim 1 wherein determining anatmospheric water content from the ratio of specific heats comprisesusing a look-up table.
 9. A method in accordance with claim 1 whereindetermining an atmospheric water content from the ratio of specificheats comprises using a look-up table relating a ratio of specific heatsto a humidity ratio.
 10. A method in accordance with claim 1 furthercomprising: recording the time and location of the measurement of atleast one of the first air temperature, the second air temperature, thefirst air pressure, and the second air pressure; transmitting each ofthe measurements, the respective time, and the respective location to aweather forecast model, and executing the weather forecast model togenerate a weather forecast using the measurement of at least one of thefirst air temperature, the second air temperature, the first airpressure, and the second air pressure.
 11. A method in accordance withclaim 10 further comprising providing the weather forecast model withatmospheric measurements from a plurality of times and locations whereinthe additional atmospheric measurements are acquired from other than thecompressor.
 12. An atmospheric monitoring system comprising: acompressor; and at least one performance sensor coupled to saidcompressor, said sensor configured to acquire atmospheric data from airchanneled through said compressor.
 13. A system in accordance with claim12 wherein said compressor is at least one of a portion of a turbineengine and a supercharger.
 14. A system in accordance with claim 12wherein said at least one sensor comprises at least one of a temperaturesensor and a pressure sensor.
 15. A system in accordance with claim 14wherein said at least one sensor comprises at least one of a compressorinlet temperature sensor and a compressor inlet pressure sensor.
 16. Asystem in accordance with claim 14 wherein said at least one sensorcomprises at least one of a compressor discharge temperature sensor anda compressor discharge pressure sensor.
 17. A system in accordance withclaim 12 further comprising a processor communicatively coupled to saidat least one sensor, said processor configured to: compute a ratio ofspecific heats from the acquired atmospheric data; and determine anatmospheric water content from the ratio of specific heats.
 18. A systemin accordance with claim 17 wherein said processor is configured toassume ideal gas behavior and isentropic compression of the airchanneled through the engine.
 19. A system in accordance with claim 17wherein said processor is configured to correct for non-ideal gasbehavior of the air channeled through the engine.
 20. A system inaccordance with claim 17 wherein said processor is configured todetermine an atmospheric water content from the ratio of specific heatsusing a look-up table.
 21. A system in accordance with claim 20 whereinsaid processor is configured to determine an atmospheric water contentfrom the ratio of specific heats using a look-up table relating a ratioof specific heats to a humidity ratio.
 22. A system in accordance withclaim 12 further comprising a processor communicatively coupled to saidat least one sensor, said processor configured to correct fornon-isentropic compression.
 23. A system in accordance with claim 12further comprising a processor communicatively coupled to said at leastone sensor, said processor configured to receive a first air temperatureand a first air pressure measured at a first location that is upstreamfrom the compressor.
 24. A system in accordance with claim 12 furthercomprising a processor communicatively coupled to said at least onesensor, said processor configured to receive a second air temperatureand a second air pressure measured at a second location that isdownstream from at least one of a compressor and a compressor stage. 25.A system in accordance with claim 12 further comprising a processorcommunicatively coupled to said at least one sensor, said processorconfigured to: record a time and a location of a measurement of at leastone of the first air temperature, the second air temperature, the firstair pressure, and the second air pressure wherein the measurements aremade substantially simultaneously; and transmit each of themeasurements, the respective time, and the respective location to aweather forecast model.
 26. A system in accordance with claim 25 furthercomprising a weather forecast model to generate a weather forecast usingthe measurement of at least one of the first air temperature, the secondair temperature, the first air pressure, and the second air pressure, aratio of specific heats derived therefrom, and a humidity ratio derivedtherefrom.
 27. A system in accordance with claim 26 wherein said weatherforecast model is configured to receive atmospheric measurements from aplurality of times and locations wherein the additional atmosphericmeasurements are acquired from other than the compressor.
 28. A methodof forecasting weather comprising: acquiring atmospheric data from a gasturbine engine onboard an aircraft during flight; processing theatmospheric data to determine an amount of water content in theatmosphere; transmitting at least one of the atmospheric data and theamount of water content to a weather forecast model; and predictingweather based on the at least one of the atmospheric data and the amountof water content.
 29. A method in accordance with claim 28 whereinacquiring atmospheric data comprises acquiring atmospheric data using asensor configured to monitor process parameters of the gas turbineengine.
 30. A method in accordance with claim 28 wherein acquiringatmospheric data comprises acquiring atmospheric data from at least aportion of the ambient air entering the gas turbine engine.
 31. A methodin accordance with claim 28 wherein acquiring atmospheric data comprisesacquiring at least one of a compressor inlet temperature, a compressorinlet pressure, a compressor discharge temperature, and compressordischarge pressure.
 32. A method in accordance with claim 28 whereinprocessing the atmospheric data comprises determining a ratio ofspecific heats of air channeled through the gas turbine engine.
 33. Amethod in accordance with claim 32 wherein processing the atmosphericdata comprises determining a humidity ratio from the ratio of specificheats.
 34. A method in accordance with claim 33 wherein determining ahumidity ratio comprises determining a water content of the air.
 35. Amethod in accordance with claim 32 wherein determining a water contentof the air comprises determining the water content of the air using alook-up table.
 36. A method in accordance with claim 28 furthercomprising stamping the atmospheric data with a time and an aircraftlocation when the data was acquired.
 37. A method in accordance withclaim 28 further comprising storing the atmospheric data with a time andan aircraft location when the data was acquired on board the aircraftfor future download.
 38. A method in accordance with claim 28 furthercomprising receiving atmospheric data at the weather forecast model froma source other than a gas turbine engine.
 39. A method in accordancewith claim 28 wherein transmitting at least one of the atmospheric dataand the amount of water content to a weather forecast model comprisestransmitting the at least one of the atmospheric data and the amount ofwater content from the aircraft to the forecast model through amulti-mode network.
 40. A method of forecasting weather comprising:determining a specific heat of a volume of air in a gas turbine engine;and determining a water content of the volume of air using the specificheat of the volume of air.
 41. A method in accordance with claim 40wherein determining a specific heat of a volume of air comprisesmeasuring a first air temperature and a first air pressure at the firstlocation.
 42. A method in accordance with claim 40 wherein determining aspecific heat of a volume of air comprises measuring a second airtemperature and a second air pressure at the second location.
 43. Amethod in accordance with claim 40 wherein determining a water contentof the volume of air comprises computing a ratio of specific heats fromthe first and second air temperatures and the first and second airpressures.
 44. A method in accordance with claim 40 wherein determiningan atmospheric water content from the ratio of specific heats comprisesusing a lookup table.